Level control means



y 1962 o. v. MURPHY ETAL 3,036,736

LEVEL CONTROL MEANS Filed Dec. 18, 1958 3 Sheets-Sheet 1.

T WW E "HHHHIIII (l I 36 39 46 34 I 22' S Fig. 5.

LOW VOLTAGE GENERATOR, CURRENT T0 DETECTOR AND CONVEYER CONTROL UNIT MOTQR CONTROL llO V 60% Fig. 2.

Fig. I.

I WIT Win11" 2 INVENTORS OSCAR l MURPHY BY GLEN/V MEYER QWMM A TTOR/VEYS 0. v. MURPHY ETAL 3,036,736

LEVEL CONTROL MEANS May 29, 1962 3 Sheets-Sheet 3 Filed Dec. 18, 1958 0 s m Y E E m Y N "a 8 VUE R O m o B m v T F RN Jr ml mm .l L A H G 9 a 2 w United States atent P lQQ 3,036,736 LEVEL CONTROL MEANS Oscar V. Murphy and Glenn Meyer, Newaygo, Mich, assignors t Newaygo Engineering Company, Newaygo, MiclL, a corporation of Michigan Filed Dec. 18, 1958, Ser. No. 781,376 12 Claims. (Cl. 22223) This invention relates to foundry equipment. More particularly, it relates to level control means especially suitable for foundry sand hoppers and the like.

In the manufacture of sand molds in large scale foundry operations, it is customary to prepare the sand on a continuous basis and to deliver the prepared sand to a number of storage hoppers from which sand is withdrawn as needed by the molder and introduced into the individual flasks. It is necessary that the sand in the flasks conform to rather rigid specifications with regard to certain physical characteristics, a most critical one of which is moisture concentration. Because the moisture concentration tends to change with time under storage conditions, the sand is usually prepared and delivered to the hoppers with the moisture concentration adjusted for a predetermined storage period.

Because of the moisture factor and because of variable sand use rates in large scale foundry operations, it is customary to charge each hopper with sand from a conveyor, such as an overhead belt, on a batch-wise basis whenever the sand in the hopper reaches a minimum level.

Aside from the moisture factor, difficulties have been encountered in many instances because of too much sand in the hopper. In such instances, sand in the lower levels of the hopper becomes excessively packed and excessive bridging occurs. This can cause substantial downtime at the mold station until the sand bridges can be broken as by the time honored method of rapping the hopper with a sledge hammer and the like. Consequently, it is customary to fill foundry sand hoppers up to a predetermined maximum level whereat substantial bridging does not occur under normal operative conditions.

Thus, in operating sand hoppers, there is a problem of determining when the minimum level has been reached and, in charging sand to the hopper, when the preferred maximum level has been reached. Another problem of controlling the conveyor in accordance with these levels is also involved.

Visual observation and manual control offer -a possible approach to a solution of these problems but, considering hopper location and position, operating personnel and the labor cost involved, this approach is not desirable.

Another app-roach to a solution of these problems has been the use of mechanical systems. These have not been satisfactory because moving parts therein become clogged with sand, requiring excessive maintenance and adjustment. Further, they have proved to be undependable, requiring firequent supervision.

Still another possible approach to a solution of these problems is an electrical system. Electrical systems that have been developed heretofore, however, are not satis factory for a variety of reasons. One type of system heretofore developed has involved high electrical potentials which have been applied in a fashion as to be extremely hazardous to life. Generally, the electrical systems heretofore developed readily and frequently get out of mechanical adjustment, primarily because of massive sand movement. Not only are false indications of sand level given by such systems because of such maladjustment but also electrical short circuits have even occurred. Moreover, such systems as have been developed are substantially effected by fluctuations in the moisture content of the sand. This is an acute problem in such systems because there is a wide variation in sand moisture conditions from one foundry operation to another and from one kind of molding sand to another.

Heretofore, electrical sensing devices for sand level control have, out of necessity, been custom designed for each foundry and even then the results have not been entirely satisfactory. Furthermore, their moisture sensitivity has necessitated revision whenever the foundry changed its molding operations in a manner resulting in the use of sand of a different moisture content.

A frequent problem with various conventional controls now in use is failure to prevent overloading of the hopper. This causes sand to spill over on personnel. It makes the area. around the hopper dirty, hazardous and sometimes ruins existing molds.

A general object of this invention is to provide an electrical system for controlling the sand level in sand hoppers, which has none of the shortcomings of the prior art systems.

A primary object of this invention is to provide an electrical, level sensing apparatus which is dependable and relatively unaffected by fluctuations in the moisture content of the sand.

A specific object of this invention is to provide an electrical, level sensing apparatus wherein dangerous, high voltages are avoided.

Another specific object of this invention is to provide an electrical, level sensing apparatus which can not get out of adjustment even under the most severe of normal operative conditions.

Still another specific object of this invention is to provide an electrical system for determining the sand level in a sand hopper and for automatically causing the hopper to be filled to a desired maximum level whenever a predetermined, minimum, sand level is reached.

A further object of this invention is an electrical sensing system capable of selecting a variety of upper and lower sand level limits.

These and other objects which may develop as this specification proceeds are achieved by this invention which shall be described with reference to the drawings wherein:

FIG. 1 is a plan view of a preferred embodiment of a sand level probe structure of this invention;

FIG. 2 is a front elevational view of the top, intermediate and bottom portions of the probe structure, which view is taken along the lines 2-2 of FIG. 1, and which view shows the probe structure in association with unit comprising a low voltage generator, current detector and conveyor motor control;

FIG. 3 is a diagrammatic view showing a preferred embodiment of a low voltage generator, current detector and motor control unit;

FIG. 4 is a front elevational view of a modification of the probe structure of FIG. 2;

FIG. 5 is a side elevational view of the terminal lead involved in the modification shown in FIG. 4;

FIG. 6 is a front elevational view of another preferred embodiment of a sand level probe structure of this invention;

FIG. 7 is a front sectional view of an electrode structure in the embodiment of FIG. 6;

FIG. 8 is a front elevational view of another preferred embodiment of a sand level probe structure of this invention; and

FIG. 9 is a front elevational view showing a sand level probe arrangement of this invention.

In general, the drawings discloses an automatic, electrical, sand level control apparatus based on a principle of operation that sand with a moisture content will conduct an electrical current. It is based on the additional principle that the shorter the distance electric current has to travel through sand with a moisture content, the lesser the electrical resistance.

The apparatus illustrated comprises broadly a sand level sensing section having a sand level probe structure. The probe structure is electrically associated with a low voltage source or generator and an electric current detector. Means are also shown in association with the current detector for indicating the sand level and for controling the sand delivery system.

The probe structure basically comprises at least two electrode sections. The sections are spaced from one another by a distance corresponding to the distance between a predetermined, maximum sand level and a predetermined, minimum sand level.

Each electrode section comprises a pair of electrode means which are arranged in a fixed, predetermined, spatial relationship to one another dependent upon the voltage generated by the low voltage source, the sensitivity of the electric current detector, the range of sand resistance normally encountered and the normal maximum distance of unsupported sand bridges. In general, we have found that the optimum arrangement of the electrode means is coplanar with the electrode means being spaced from one another by a distance in the range from about three inches to about five inches. One of the electrode means in each pair is electrically connected as by a common lead to one side of said low voltage source. Each-of the remaining electrode means is electrically connected by a separate, electrical circuit to the other side of said source of low voltage.

The electric current detector comprises means associated with each of said separate electrical circuits for detecting the passage of current therethrough.

Thus, with reference to FIGS. 1-5, there is illustrated a sand level sensing and locating apparatus. comprising a sand level probe structure 20, a unit 46 comprising a low voltage generator, current detector means and sand conveyor control means, and electrical leads between the probe structure 20 andthe unit 46.

Probe Structure The probe structure 20 illustrated in FIGS. 1-5 is suitable for most foundary sand hoppers. It comprises a-low'voltage, linear, 'bus'bar electrode 22 having a bus,

bar lead 24 joined thereto at the top end thereof. Along the length of the bus bar and spaced apart therefrom on a line parallel to the bus bar is a top electrode element 26, an intermedate electrodeelement 28 and a bottom electrode element 30. The illustration in FIG. 2 of three electrodesis merely illustrative since the intermediate electrode may be omitted or additional intermediate electrodes may be added.

The top electrode element 26 is spaced from the bottom'electrode element 30 by a distance corresponding to the distance between a predetermined, normal operative, maximum sand level and a predetermined, normal operative, minimum sand level of the sand hopper to which the invention is to be applied. The spacing of the intermediate electrode element 28 from the top and bottom electrode elements 26 and 30 will usually be equidistant, although not necessarily so, particularly-where an additional intermediate electrode element is used.

The top electrode element 26 is separated from the intermediate electrode element 28 by a rigid tube 32'formed from an electrically non-conductive material. The bottom electrode element 30' is separated from the intermediate electrode element 28 bya rigid tube 33 of nn conductive material.

Asshown in FIGS. 2 and 4, the top-and intermediate electrode elements 26 and 28 are actually in the form of metallic, thin wall couplers which engage the respective spacer tubes in press fit. The electrode elements and the spacer tubes could also be threadedly joined for easy assembly and separation. The elements, in any event,

should have Walls as thin as possible in order to minimize vertical sand bridging. At the same time the element walls should. have sufli'cient strength to withstand crushing from the sand./ The bottom electrode element 30 is a thin wall, metallic cap which engages the insulator tube 33 in press fit. Each electrode element in combination with the'bus bar electrode 22 comprises an individual conductor section.

The electrode element structure (FIG. 2) is supported in place by a rigid tube 34 of electrically non-conductive material, one end'of which engages the top electrode element 26 in press fit. The support tube 34 extends in press fit through a hole in a horizontally disposed, mounting block 36 of an electrically non-conductive material. It will be observed that the bus bar electrode 22 also passes in press fit through a hole in the mounting block 36. Instead of a press fit joint, the ends of the mounting block 36 may be bifurcated and the assembly of the block to the other components effected by a clamping action such as would be produced by a bolt passing through one bifurcated end and threadedly joined to the other bifurcated end. The mounting block 36 is provided with bolt holes 39 and the like for use in attaching the probe structure 20, for example, to a bracket in the sand hopper.

In FIG. 2 the spacing between the electrode elements 26, 28 and 30 and the linear bus bar electrode 22 is established and maintained by the mounting block, 36 and below the mounting block by rigid spacer rods 37 and 38, attached to the bus bar electrode 22. These rods 37 and 38 comprise ring members which are shown assurrounding and holding in press fit the respective spacer tubes 32 and 33. Both the ring members and spacer rods may be constructed of either electrically conductive material or electrically non-conductive material. As shown in FIG. 2, the ring members are constructed of electrically non-conductive material. This may be of advantage when the ring members are located close to the electrode elements and the sand has a high bridging tendency. However, such construction is not necessary under the concepts of this invention.

Each of the electrode elements 26, 28 and 30 is connected to an individual, insulated wire or lead. Thus, it will be observed that the bottom electrode element 30 is connected to a bottom electrode element lead 40, the

intermediate electrode element 28 is connected to an intermediate electrode element lead 42 andthe top electrode element 26 is connected to a top electrode element lead 44. Each of these leads passes upwardly through the spacer tubes of the probe structure into a junction box 45 at the top thereof. From the junction box 45 the leads 40, 42 and 44 alongwith the bus bar electrode lead 24 run to the low voltage generator, current detector and control unit 46. While the leads from the bus bar electrode 22 and the'electrode elements may run directly to the unit 46 as in FIGS. 2 and 3, it should be realized that such leads may also involve a plug and socket arrangement as, for example, at the junction box 45. This is of advantage in adapting the apparatus to local conditions.

The electrode elements 26 and 28 may be as shown in FIG. 2. They may also be as shown in FIG. 4. In this form, using the element 28 as an example, there is provided an inwardly extending, annular ridge 112. In assembling the probe structure, the ends of the spacer tubes 32 and 33 are seated against the annular ridge. This embodiment has an advantage over the embodiment of FIG. 2 in that there is greater structural strength and a positive seating therein of the spacer tubes. It also facilitates assembly and enables provision to be made for a binding post type connection to the corresponding electrical lead, which may not always be feasible with the embodiment of FIG. 2.

The electrical leads for the various electrode'elements.

26, 2-8 and 30 and bus bar electrode 22 may be connected as by a solder joint as shown in FIG. 2. This type of connection has a disadvantage, however, in that there may be some sacrifice in ease of assembly and in ease of change-over for different operative sand levels. Accordingly, the electrical lead connection may be made as by a conventional binding post assembly such as illustrated in FIGS. 4 and 5 in conjunction with electrode element 28 for example. In this type of connection, a threaded hole 114 is provided in the inner wall of the electrode element, in this embodiment preferably in the annular ridge member 112. A round, flat head, terminal lead 118 is soldered to the wire of the lead 42. The head 118 is then placed over the hole 114 and the binding post 1 16 with appropriate washers if desired is inserted through the head 118 into the hole 114 and screwed down until the connection is tight.

Materials of construction used in the probe structure 20 are conventional. The electrically non-conductive material used in the insulator tubes 32, 33 and 34, mounting block 36, spacer rod rings and junction box 45 may be, for example, laminated plastics comprised of paper or a fabric of cellulose, glass, asbestos or synthetic fibers bonded with ureaand pheno-formaldehyde or melamine resins and cured at elevated temperature and pressure. The Formica and Micarta materials are especially useful. The electrode elements and bus bar electrode are fabricated from electrically conductive metals, such as, for example, copper, aluminum, steel and the like. They should be of a material which is non-corrosive in the presence of damp sand and the chemicals present in the sand or plated or coated with such a material of good electrical conductivity characteristics. Otherwise, surface corrosion will impair their conductivity. Furthermore, they should be resistant to surface abrasion due to the abrasive character of foundry sand.

Electrical Circuitry The voltage generator, current detector and control unit 46, as shown in FIG. 3, involve a number of associated electrical circuits which provide a low voltage generator section 47, a power supply section 48, a current detector section 50 and a relay section 52.

The power supply section 48 comprises the usual power supply line from a suitable source of, for example, 110 volt, 60 cycle electric current. One of the power supply leads is grounded to the chassis of the unit 46 while the other lead passes to an on-off switch 54 shown in on position. A lead passes from the switch 54 to one end of the primary winding of a transformer 56. The other end of the primary winding is grounded to the chassis of the unit 46. The transformer 56 comprises the usual secondary windings, one for a vacuum tube filament circuit and the other for a vacuum tube plate circuit. One end of the plate winding is connected to an isolated ground conductor 57 which may also be described as a return lead. The other end is connected to the positive terminal of a half-wave rectifier 58, and to the negative terminal of a half-wave rectifier 64.

The half-wave rectifier 58, which may be, for example, a selenium rectifier, any suitable semi-conductor, or vacuum tube, serves the low voltage generator section 47. This section comprises an R-C network. This network involves, in series, a resistor 59, a potentiometer 60 having a slide arm 63 and a resistor 61. Connected across the series of resistances so as to be in parallel therewith is a filter condenser 62. It will be observed that the positive side of the R-C network (namely, the condenser 62 and the resistor 61) is connected to return lead 57. The negative side of the R-C network is connected to the negative terminal of the half-wave rectifier 58. Thus, the direction of current flow in the circuit is from the rectifier 58 through resistor 59, potentiometer 60 and resistor 61. Hence the potential at the slide arm 63 is negative with reference to the connection of resistor 61 to return lead 57. This potential should be in a range from about 4 volts to about -l2 volts.

The half-Wave rectifier 64, which, for example, may be a selenium rectifier or any suitable semi-conductor or vacuum tube, is connected at its positive terminal to an R-C filter network. This network comprises in parallel a resistor 66 and a filter or smoothing condenser 68, both of which are connected to the isolated ground conductor 57. The rectifier 64 is arranged in the circuit so that current passes through the resistor 66 to the rectifier 64 whereby the potential at the positive terminal of the rectifier 64 is positive with reference to the connection of the isolated ground conductor to the resistor 66. This potential should be about l50 volts and is the plate voltage or B{- potential for the vacuum tube circuits of the unit It will be observed that the bus bar electrode lead 24 is connected to the slide arm 63 of the potentiometer 69 of the low voltage generator section 47. It will also be observed that there is no electrical connection between the bus bar electrode 22 in the probe structure 20 and the individual electrode elements 26, 28 and 30 except when sand having a moisture content bridges the gap between each individual electrode element and the bus bar electrode. On the other hand, it will be observed that the individual electrode elements '26 and 28 are connected through their respective leads 44 and 42 to resistors 70 and 72, respectively, and, when armature 104 is in touch with its contact 106, that the electrode element 30 is connected through its lead 40 to resistor 74. Each resistor 70, 72 and 74 is connected to the return lead 57 (also referred to as isolated ground conductor 57). Consequently, there is, under normal operative conditions and with relay 194 in touch with its contact 106 a low potential between the bus bar electrode 22 and each of the individual electrodes. Hence, when sand bridges each gap under these conditions, current will flow through each electrical circuit thus established.

The current detector section 50 of the electrical circuit comprises the resistor 70, the resistor 72 and the resistor 74. Connected across each of the three resistors is a corresponding triode section of a vacuum tube, in each case the cathode being connected to return lead 57 and the grid being connected to the side of the resistor not connected to return lead 57. In FIG. 3, two double triode tubes 76 and 78 are used, each one, for example, being a l2AT7. In such case, each of the resistors 70, 72 and 74, preferably, are about 470 kilohms.

The first triode section of tube 76 is connected across the resistor 70 while the second triode section is connected across the resistor 74. The first triode section of tube 78 is connected across the resistor 72. The second triode section of tube 78, however, is not hooked up. It is therefore available for use in the same manner as the first triode section of tube 78 in the event an additional electrode element in the probe structure 26 is used. The filament of each tube is connected in parallel across the filament winding of the transformer 56. The voltage output of the filament winding should be 6.3 volts. Accordingly, the filament pins of the tubes 76 and 78 are connected to operate on this voltage. The plates of the triode sections of tube '76 and the plate of the first section of tube '78 are associated with the power supply 48, particularly with the positive terminal of the rectifier 64 wherefore, under normal operative conditions, the volt potential is applied to the respective plates.

Under normal operative conditions, without passage of current through the grid resistors 70, 72 and 74, each of the corresponding triode sections should be at substantially a zero volt grid bias and each of said triode sections will be conducting current. Passage of current through each of the grid resistors 70, '72 and 74, however, creates a negative grid bias (because of the potential at slide arm 63 and resultant current flow through the resistor return lead '7) which will shutoff the current flow through the corresponding triode sections.

The relay section 52 of the unit 46 as shown in FIG. 3 comprises a relay associated with the plate circuit of each of the three triode sections of the vacuum tubes 76 and 78. More specifically, it will be observed that the plate of the first triode section of tube 76 is connected to one terminal of a relay solenoid 80. The other terminal of relay solenoid 80 is connected to the positive terminal of the rectifier 64 (the B+ terminal of the power supply 48). The plate of the second section of tube 76 is connected to one terminal of a relay solenoid 82, the other terminal of which is connected to the B+ terminal of the power supply 48. The plate of said first triode section of vacuum tube 78 is connected to one terminal of a third relay solenoid 84. The other terminal of the solenoid 84 is connected to the 13+ terminal of the power supply 48.

Relay solenoid 80, when energized, actuates a relay armature 86 which is connected to a conveyor motor control lead 87 the armature 86 has an energized position contact 88 and a de-enerized position contact 89. The energized position contact 88is connected to contact 94 associated with the relay armature 96. As shown, the deenergized position contact 89 is unconnected. The motor control lead 87 passes into a conventional motor control unit 19 comprising a magnetic starter and the like, which unit 19 has a return lead grounded to the chassis of the low voltage generator, current detector and control unit 46.

Solenoid 80 also actuates a relay armature 90 which is connected to the HO volt lead 53. The armature 90 has a deenergized position contact 91 and an energized position contact 92. As shown, the de-energized position contact 91 is unconnected while the energized position contact 92 is connected to one side of an indicator light 93, the other side of which is grounded to the chassis of the unit 46.

Relay solenoid 82 actuates an armature 9 6 which is connected to the 110 volt lead 53. This armature has an energized position contact 94 and a de-energized position contact 95. The energized position contact 94 is connected as already indicated to the contact 8 8 of the first described relay. The de-energized position contact 95, as shown, is unconnected. 7

Relay solenoid 82 also actuates an armature 98 which is connected to the 110 volt lead 53. The armature 98 has a de-energizedposition contact 99 and an energized position contact 100. As shown, the de-energized posi tion contact 99 is unconnected while the energized position contact 100 is connected to one terminal of indicator light 111. The other terminal of the indicator light 111 is grounded to the chassis of unit 46.

Relay solenoid 84 actuates an armature 108 which is connected to the 110 volt lead 53. This armature has an energized position contact 109 and a de-energized position contact 110. As shown, the energized position contact 109 is connected to one sideof indicator light 101, the other side of which is grounded to the chassis of unit 46.

Another relay circuit is provided in relay section 52. This circuit comprises a solenoid 102, one terminal of which is connected to the motor control lead 87 and the other terminal of which is grounded to the chassis of the unit 46. The solenoid 102 actuates an armature 104 which is connected to the grid of the second triode section and to the resistor 74. The armature 104 has an energized position contact 104 and a de-energized position contact 106. As shown, the energized position contact 104 is unconnected while the de-energized position contact 106 is connected to the bottom electrode element lead 40. 7

Operation A conventional sand hopper station in foundries comprises, as diagrammatically shown in FIG. 3, a sand hopper 10 having a bottom discharge passageway 12 in combination with a discharge gate'1 4 which can be opened and closed as desired by the molder'. Associated with the sand hopper is a sanddelivery system such as, for example, an overhead conveyor 16 of the belt type, which is driven by a conveyor motor 18:.in1combination with a conveyor motor control unit 19. Where several hoppers are supplied from a single belt, a sweep or plow is provided at each hopper. These may be actuated to swing across the belt or to lower upon the belt to cause the sand to discharge from the belt into the selected hopper. When such structuresare utilized, the motor 18 may be replaced by a solenoid or other prime mover. This, however, does not affect this invention. The conveyor motor control unit 19 comprises, for example, a solenoid starter switch which functions to switch on andto switch off electric current to the motor. The starter switch itself is actuated by volt, 60 cycle current which heretofore was turned on and off only by a manually operated switch. In this embodiment of the invention, current to the starter switch in unit 19 is controlled by the low voltage generator, current detector and control unit 46 having the 110 volt, 60 cycle, on-oflf switch 54.

To use theapparatus of FIGS. l-S, the probe structure 20 is mounted in the sand hopper 10 with the bus bar electrode 22 in vertically disposed position and with the bottom electrode element 30 at a predetermined, normal operative, minimum sand level L, the intermediate electrode element 28 at an intermediate level L and the top electrode element 26 at a predetermined, normal operative maximum sand level L. Care must be taken that the electrode elements and bus bar electrode do not touch the sides of the hopper, in order to avoid short circuiting the electrodes. The switch 54 is then closed or fturned on and the apparatus is in operation.

Assuming that operation is started with the hopper completely empty of sand, it will be apparent that there is no electrical connection established between the bus bar electrode'22 and the individual electrode elements 26, 28 and 30. Consequently, there is no electrical current flow through the grid resistors 70, 72 and 74. Accordingly, each of the three triode sections is conducting current whereby the solenoids 80, 82 and 84 are energized and,

the armatures 86, 90, 96, 98 and 108 are actuated into position with their respective energized position contacts 88, 92, 94, 10 0 and 109. As a result the indicator lights 93, 101 and 111 are turned on, the motor control unit 19 is energized intostarting the conveyor drive motor 18, and relay solenoid 102 is energized, causing its armature 104 to be actuated into energized position. i

a As sand 11 is delivered by the conveyor 16 into the hopper 10, the sand level reaches the predetermined minimum level L and the sand bridges and gap between the bus bar electrode 22 and the bottom electrode element 30. However, no current flows therethrough and through the bottom electrode element lead 40 because of the open circuit between de-energized position contact 106 and armature104. Consequently, thesecond triode section of vacuum tube 76 continues to conduct current.

When the sand level in the hopper reaches the intermediate level L, as-in FIG. 3, the gap between the bus bar electrode 22 and the intermediate electrode element 28 is bridgedv with sand, completing a current path from the slide arm 63 through resistor 72 whereby a negative bias is created at the grid of the first triode section of vacuum tube 78. The first triode section thereupon ceases to conduct current. Thus solenoid 84 becomes de-energized and armature 108 snaps into de-energized position, thereby opening thecircuit of the indicator light 101 which goes out.

.When the sand level in the hopper reaches the predetermined maximum level L", the gap between the bus bar electrode 22 and the intermediate electrode element 26 is bridged with sand 1'1. This completes the electrical circuit from slide arm 63 to resistor 70 and causes current to flow through said resistor. This creates a negative bias on the grid of the first triode section of the tube 76 and causes. the first triode section to cease conducting current. Relay solenoid 80 is thereby de-energized and armatures 86 and '90 move into their de-energized positions. This breaks the circuit of the L" indicator light 93 which goes out, the circuit of the motor control unit 19 whereby the conveyor motor 18 is turned oil, and the circuit of the relay solenoid 102 whereby the armature '4 snaps to its de-energized position. This latter action completes the circuit from slide arm 63 to grid resistor 74 with the result that current flows through the grid resistor 74. A negative bias is thereby created on the grid of the second triode section of vacuum tube 76 and the how of current therethrough is stopped. Solenoid 82, consequently, is de-energized and armatures 96 and 98 snap back into their de-energized positions. This opens another portion of the circuit of the motor control unit 19. In addition, the circuit of the L indicator and motor light 111. is opened and the light goes out.

At this point in the normal operative cycle of the apparatus as shown in FIGS. 1-5, all indicator lights should be out and the conveyor motor 18 ofiF. However, should the lights flicker on and off and the relays chatter, the slide arm 63 should be moved just to the point on the potentiometer 60 of greater negative potential (with reference to the construction of return lead 57 to resistor 61) whereat the relays drop out and do not chatter, and no higher. As pointed out previously herein, however, the maximum negative potential should not, and need not, be greater than about -12 volts. Normally, the potential will be somewhat less.

As sand is discharged from the hopper 10 via discharge outlet 12, the sand level recedes below the level L, thereby producing a gap between the low voltage bus bar electrode 22 and the top electrode element 26. This interrupts the current flow through resistor 70 whereby the negative bias on the grid of the first triode section of the vacuum tube 76 is discontinued. The first triode section thereupon commences to conduct current. Solenoid 80 is energized and armatures 86 and 90 are actuated into energized position with their energized position contacts 88 and 92, thereby connecting the motor control unit lead 87 with contact 94 and completing the circuit of the L" indicator light 93 which goes on.

When further discharge of sand from the hopper 10 brings the sand level below the level L, the current path between the bus bar electrode 22 and the electrode element 2% is broken. Current flow through grid bias resistor 72 accordingly ceases whereupon the first triode section of vacuum tube 78 conduts current which energizes relay solenoid 84. Armature 108 snaps into its energized position with its energized position contact 109 whereby the circuit of the L indicator light is completed and the light 101 goes on.

When the sand level in the hopper recedes below the minimum level L, the sand bridging the gap between bus bar electrode 22 and the electrode element 30 falls away, thereby stopping the current flow through the circuit of grid resistor 74. The second triode section of vacuum tubes 76 accordingly starts conducting current and solenoid 82 becomes energized. Armatures 96 and 98 snap into energized position thereby completing the circuit of the motor control unit 19 (whereby the conveyor motor 18 is turned on and relay 102 is energized, causing armature 104 to move to energized position) and the circuit of the L level and motor indicator light 111 (which likewise goes on), thus commencing a new cycle of operation.

To stop the operation of the apparatus, all that need be done is to open the main switch 54.

The electrical circuit of FIG. 3 can be modified so that the level indicator lights 93, 101, and 111 function in reverse. Thus, the lead to the L" indicator light 93 may be connected to the de-energized position contact 91 rather than to the energized position contact 92; the lead to the L indicated light 101 may be connected to the de- 10 energized position contact rather than to the energized position contact 109, and the lead to the L and motor indicator light 111 may be connected to the deenergized position contact 99 rather than to the energized position contact 100.

Under these conditions, when the hopper 12 is filled to the normal operative maximum level L" with sand all of the indicator lights are on. When the sand level falls below the level L, the L indicator light 93 goes ofi. When the sand level falls below the level L, the L' indicator light 101 goes off. When the sand level falls below the normal operative minimum level L, the L and motor indicator light goes off. As the sand level in the hopper 12 is raised past the minimum level L, the L and motor indicator light stays ofi because of the armature 104 being in energized position. As the sand level is raised past the intermediate level L, the L indicator light 101 goes on. When the said level again reaches the maximum level L, the L" indicator light 93 goes on and the L indicator light goes on.

Other Embodiments Under some circumstances, the probe structure 20 of FIGS. 15 may not be practical or Wanted. This may be particularly true in the case of shallow hoppers or bins and in the case of extremely deep bins. In these instances the probe structures of FIGS. 6, 7 and 8 are useful.

The probe structure of FIGS. 6 and 7 utilizes the side wall 132 of the hopper as the basic support means. In this embodiment the electrode means of each pair are vertically positioned in relation to one another, the optimum distance between the electrode elements in each pair preferably being in a range of from about three to about five inches.

In particular it will be observed that the probe structure of FIGS. 6 and 7 comprises a pair of electrode elements 22a and 26a at the normal operative maximum sand level L, a pair of electrode elements 22b and 28a at an intermediate sand level L, and a pair of electrode elements 22c and 30a at the normal operative minimum sand level L. As shown each of the electrode elements is in the form of a thin wall, electrically conductive metal cap mounted on the end of a horizontally disposed support tube of electrically non-conductive, rigid, sturdy, material. Thus, electrode element 22a is mounted on the end of a support tube 122a. Electrode element 26a is mounted on the end of a support tube 126. Electrode elements 22b and 28a are mounted on the ends of support tubes 12212 and 128, respectively, and electrode elements 22c and 30a are mounted on the ends of support tubes 1220 and 130.

Each of the support tubes pass through suitably disposed holes in the side wall 132 of the hopper and are secured thereto. Thus, for example, it will be observed in FIG. 6 that support tubes 1220 and pass through holes 134 and 136 in the Wall 132. On the outside of the Wall 132 eaclrtube passes through a mounting flange 138 attached to the wall. By means of a set screw 139 (FIG. 7) in each flange the distance of the electrode elements from the wall 132 may be adjusted. In general this distance should be in the range of about nine to twelve inches.

Each electrode element of the embodiment of FIGS. 6 and 7 is connected to an electrical lead. Thus, electrode element 30a is connected to the electrical lead 40, electrode element 28a is connected to the electrical lead 42, and electrode element 26a is connected to electrical lead 44. Electrode element 220 is connected to the common electrical lead 24 While electrode elements 22a and 22b are connected as by leads 24a and 24b, respectively, to the common electrical lead 24.

The same considerations mentioned with respect to the probe structure of FIGS. 1-5 in reference to materials of construction and to attaching together the various struc- 1 l tural elements also apply in thecase of the embodiment of FIGS. 6 and 7. p The operation of the embodiment of FIGS. 6 and 7 is substantially the same as the embodiment of FIGS. 1-5.

The probe structure'of FIG. 8' utilizes the cross beams of the hopper 10 as support. In this embodiment the electrodes are again vertically disposed with the optimum spacing in between. In the embodiment of FIG. 8, the hopper 10 comprises cross beams at different levels therein, a bottom discharge passageway 12 and a discharge gate 14. On the bottom side of the beam nearest the normal operative, maximum sand level, here shown as beam 150, and a substantial distance away from the side wall of the hopper 10 is a probe assembly 152. On the bottom side of the beam nearest the normal operative, minimum sand level, here shown as beam 151, and a substantial distance away from the side wall of the hopper 10 is a probe assembly 154.

The probe assembly 152 comprises electrode elements 22a and 26a mounted respectively on the ends of support tubes 122a and 126. The electrode elements 22a and 26a again may be in the form of thin wall, conductive metal caps while, the support tubes can be either electrically nonconductive or conductive. The support tubes 122a and 126 are embedded in an electrically nonconductive mounting block 153 suitably fastened to the cross beam 156. Insulated electrical leads connected to the electrode elements (or tubes if electrically conductive) pass through the block 153 into a protective conduit 155 leading out of the hopper 10 as through a suitably positioned hole in the side wall thereof to the unit 46. The lead from the electrode element 22a is connected to the common electrode lead 24. Electrode element 26a is, of course, connected to the electrical lead 44.

Similarly, the probe assembly 154 comprises electrode elements 22c and 30a, which are mounted respectively on the ends of support tubes 1220 and 130. The tubes are embedded in, and suspended from, an electrically non-conductive block 155 suitably fastened to the cross beam 151. Electrode element 22c (or tube 1220 if electrically conductive) is connected to the common electrical lead 24 while the electrode element 300! (or tube 130 if electrically conductive) is connected to the electrical lead 40. Both leads pass from the block 155 through a protective conduit 156 leading out of the hopper 10 to the unit 46.

The operation of the probe assembly is in substance the same as described with reference to the embodiment of FIGS. 1-5. In the embodiment of FIG. 8, however, no probe assemblyfor an intermediate sand level has been shown. However, if desired, such can be provided in a similar manner if an intermediate cross beam is present and if not, the embodiment of FIGS. 1-5 or the embodiment of FIGS. 6-7 can be utilized.

The embodiment of FIG. 9 concerns the double bin type of sand hoppers having two discharge passageways 12a and 12b and two corresponding discharge gates 14a and 14b, and having a single sand delivery system. Two separate probe structures connected in parallel with the unit 46 can be used in this situation. However, it is much simpler to use an auxiliary probe structure 140 in series with a single probe structure 20. In the embodiment of FIG. 9 the auxiliary probe structure 140 comprises a pair of electrically conductive, electrode bars 142 and 143 spaced apart, preferably by the optimum distance of three to five inches. To establish and maintain the spacing insulator blocks 144, 145 and 146 are provided with the bars 142 and 143 passing through them. Connected to the electrode bar 142 is the common lead 24. Connected to the electrode bar 143 is an auxiliary lead 214d which is connected to the bus bar electrode 22 of the probe structure 20 in place of the common lead 24.

. To use the embodiment of FIG. ,9, the auxiliary probe structure 140 is mountedinonebin section of the hopper and the probe structure 'is mounted in the other bin section of the hopper. Preferably; the probe structure 20 is placed in the bin section-requiring a higher frequency of filling if such a condition exists The electrical leads 24, 40, 42 and 44, of course, go to the unit 46. Under normal operation conditions the probe structure 20 will function as before as long as there is sand between the tips of the electrode bars 142 and 143. However, as soon as sand falls away from the tips of the electrode bars 142 and 143 all of the electrical circuits of the probe structure 2% are broken and unit 46 operates to actuate the sand delivery system until once again sand forms an electrical circuit from the electrode bar 142 to the electrode bar 143 of the auxiliary probe structure 140 and sand bridges the gap, if any, between the bus bar electrode 22 and the elect-rode element 2.6 of the probe structure 20.

As previouslynoted herein, it is important that the corresponding electrode means in the probe assembly of this invention be spaced apart by an optimum. distance. in the range of about three to about five inches. A distance less than three inches should not be used because of the likelihood of sand bridges being formed which do. not collapse as the sand level falls away, thus nullifying the operation of the apparatus. inches, the possibility of such bridges is quite remote.

' A distance in excess of five inches should not be used because of the large resistance of the current path between the electrode. means, particularly in. relatively dry sand. In other words, the resistance is so large that with the low potential involved, the current flow is insufficient to create across the grid resistors 70, 72 and 74 the requisite tube current cut-off voltages.

i The concepts of this invention olferrahumber of important advantages. tures can be readily fabricated, assembled, and marketed as a. packaged unit with theprobe structure being readily preset at the time of fabrication to the local requirements of hopper design and sand levels. are rugged and sturdy, and do not readily get out of adjustment. Indeed, all that the foundry operator need to do is installthe probe structure and the unit 46, operate the line switch andadjustthe slide arm 63, if necessary. The electrical circuitry is sufliciently flexible that addi-. tional circuitry can be readily added to locate and indicatemore than one intermediate level, the wiring and components beingsimilar to that found in the first grid section of vacuum tube 78, or all intermediate level circuitry eliminated without upsetting the basic operation. Also, relatively simple wiring changes permit an intermediate electrode to shut-off the conveyor motor, if it is desired to limit maximum sand level to only a'portion of the hoppers capacity. Finally, because of the exceptionally. low voltage involved in the probe structure, and because of'the return lead or isolated ground 57 in the unit 46, the assembly offers no hazard to personnel working around sand hoppers provided with the probe structure of this invention.

As this invention may be embodied in several forms without departing from the spirit on essentialcharacteristics thereof, the present embodiment istherefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of theclaims, or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

We claim:

1. As an article of manufacture, a probe structure for sensing the sand level in a foundry sand hopper and the like, which comprises: at least'two conductor sections longitudinally aligned and spaced from one another by a distance corresponding to .the distance between a predetermined, normal operative, maximum sand level in a hopper and a predetermined, normal, operative, minimum In the range of three to five.

In the first place, the probe struc-- The probe structures.

sand level in a hopper, each section comprising a pair of electrode elements which face each other laterally and which are laterally spaced from one another by a distance in the range from about three inches to about five inches, one of said elements in each pair comprising a straight, longitudinal, common, bus bar electrode, the electrode element at said maximum sand level comprising a thin wall, cylindrical, metallic coupling, and the electrode element at said minimum sand level comprising a thin wall, cylindrical, metallic cap; tubing of electrically nonconductive material between said coupling and said cap and seated in the same; means inside of said tubing and connected to said coupling for conducting electrical current; means inside of said tubing and connected to said cap for conducting electric current; means connected to said bus bar electrode for conducting electric current; means for establishing and maintaining the spacing be tween said bus bar electrode and said remaining electrode elements; and means for mounting said bus car electrode and said tubing comprising said electrode elements in a sand hopper.

2. A probe structure for sensing sand levels in a foundry sand hopper and the like, which comprises: a straight, bus bar electrode; a lead wire associated therewith for connecting the same to one side of a low voltage source; a length of enclosed, hollow tubing disposed parallel to said bus bar and spaced apart therefrom by a distance in the range from about three inches to about five inches, said tubing being divided along the length thereof into alternate, electric current conductor and nonconductor sections with a conductor section at one end thereof and the remaining conductor sections spaced therefrom along the length of said tubing at distances corresponding to predetermined, normal operative, sand levels in a hopper; a separate lead wire associated with each of said conductor sections for connecting the same to circuits associated with the other side of said low voltage source; means rigidly securing said bus bar to said tubing and said bus bar being a structural support for said tubing; means for mounting the combination of said bus bar electrode and tubing in a foundry sand hopper.

3. An apparatus for controlling the sand level in a foundry sand hopper and the like and having a sand delivery means, which comprises: a level sensing section having a probe structure electrically associated with a low voltage source; said probe structure comprising a structural straight, rod-like, common bus bar electrode, a lead wire associated therewith for connecting the same to one side of said low voltage source; a length of straight, enclosed, hollow tubing disposed parallel to said bus bar and spaced apart therefrom by a distance in the range from about three inches to about five inches, said tubing having an electric current conductor section corresponding to a predetermined, normal operative, minimum sand level in said hopper, an electric current conductor section corresponding to a predetermined, normal operative, maximum sand level in said hopper and an insulator section between said conductor sections; a lead wire connected to said minimum sand level conductor section and to a circuit associated with the other side of said low voltage source; a lead wire connected to said maximum sand level conductor section and to another circuit associated with said other side of said low voltage source; means for mounting the combination of said bus bar electrode and tubing in said foundry sand hopper; rigid means secured to both said tubing and said bus bar electrode for establishing and maintaining the spacing of said tubing from said bus bar electrode; said bus bar electrode supporting said tubing; current detector means in each of said circuits for detecting passage of electrical currents therethrough and thus between said bus bar electrode and corresponding conductor sections; and, means in association with said current detector means for actuating the sand delivery means for said hopper when passage of current between said bus bar electrode and said bottom conductor section ceases and for stopping sand delivery by said sand delivery means when passage of current commences between said bus bar electrode and to said conductor section at said predetermined, normal operative, maximum sand level in said hopper.

4. An apparatus for indicating the sand level in a foundry sand hopper and the like and haw'ng a sand delivery means, which comprises: a level sensing section having a probe structure electrically associated with a low voltage source; said probe structure comprising a straight, bus bar electrode, a lead wire associated therewith for connecting the same to one side of a low voltage source, a length of straight, enclosed, hollow tubing disposed parallel to said bus bar and spaced apart therefrom by a distance in the range from about three inches to about five inches, said tubing having a bottom, electric current conductor section corresponding to a predetermined, normal operative, minimum sand level in said hopper, a top, electric current conductor section corresponding to a predetermined, normal operative, maximum sand level in said hopper, an intermediate, electric current conductor section intermediate said bottom conductor sections and said top conductor section and insulator sections between said conductor sections; lead wires connected to each of said conductor sections and to corresponding circuits associated with the other side of said low voltage source; means for mounting the combination of said bus bar electrode and tubing in said foundry sand hopper; means for estab lishing and maintaining the spacing of said tubing from said bus bar electrode; means in said circuits for detecting passage of electrical current therethrough and thus between said bus bar electrode and the corresponding conductor sections; and means associated with each of said current detecting means for actuating a corresponding level indicator light according to the passage and non-passage of electric current therethrough.

5. An apparatus according to claim 4, which comprises: means in association with said current detector means for actuating the sand delivery means for said hopper when passage of electrical current between said bus bar electrode and said bottom conductor section ceases and for stopping sand delivery by said sand delivery means when passage of electrical current commences between said bus bar electrode and said conductor section at said predetermined, normal operative, maximum sand level in said hopper.

6. A sand level probe for sand hoppers, said probe comprising: a pair of elongated, rod-like elements and electrical insulating means at spaced intervals along said elements for rigidly spacing said elements from each other throughout their length; one of said elements having electrodes spaced therealong; said electrodes being electrically insulated from each other; individual conductor means secured to each of said electrodes; the other of said elements having exposed electrode portions aligned lengthwise of said elements with each of the electrodes of said one element; said other element being a structural support for said one element.

7. A sand level probe for sand hoppers, said probe comprising: a pair of elongated, rod-like elements and means at spaced intervals along said elements for rigidly spacing said elements from each other in parallel relationship throughout their length; one of said elements having electrodes spaced therealong; said electrodes being electrically insulated from each other; individual conductor means secured to each of said electrodes; the other of said elements having exposed electrode portions aligned lengthwise of said elements with each of the electrodes of said one element; said other element being a structural support for said one element.

8. A sand level probe for sand hoppers, said probe comprising: a pair of elongated, rod-like elements and means at spaced intervals along said elements for rigidly spacing said elements from each other throughout their length; one of said elements having electrodes spaced therealong; said electrodes 'being electrically insulated lfromeach other; individualconductor means secured to each of said electrodes;'the other of said elements being 'of electrically conductive'mate'rial and a structural support for said one element.

9. A sand level apparatus'for sandhoppers comprising: a pair of elongated, rod-like elements and means .at

spaced intervals alongsaid elements for rigidly spacing said elements 'from each other throughout their length; one of said: elements having electrodes spaced therealong; said electrodes beingelectrically insulated J from each other; indivi'dualconductor means secured to each of said electrodes; the other of said elements having exposed electrode portions aligned lengthwise of said elements with each of the electrodes of said one element;

.said other element being a structural support for said one element; a source of. low voltage current electrically connected to said spaced electrodes for generating signals thereacross;'and a signal receiving means electrically connected to said current source and said spaced electrodes .for utilization of said generatedsignals.

10. A sand level probe fora hopper, said generator comprising: a pair of elongated, rod-like elements and means at spaced intervals along said elements forrigidly spacing said elements from each other throughout their length; collars surrounding one of said elements at spaced intervals therealong; saidcollars being of electrically conductive material and electrically insulated 'from each other; separate conductor means secured to each of said collars; the other of saidelements having exposed electrode portions aligned lengthwise ofsaid elements with each of said collars; saidother element being'arigid structural support for said one element.

11. In combination with a sand hopper having a pair of substantially spaced discharge gates, a sand levelsignal generator, for indicating the level of sand adjacent said gates comprising: adjacent oneof said gates a-tpair of elongated, rodrlike elements and means atspaced intervals structural support for said one element; a pair of spaced detector electrodes mounted in said hopper adjacent the other of said gates and means supporting said electrodes in spaced relationship to each other adjacent the bottom of said hopper; said detector electrodes being spaced from said rod-like elements a distance suflicient to permit sand in said hopper to electrically insulate them from each other; and a low voltage current source electrically across said rod-like elements and said spaced electrodes; said detector electrodes being connected in series between said current source and said other element whereby the sand between said detector electrodes forms part of the electrical circuit between said current source and said other element.

12. In combination with .a sand hopper having a pair of substantially spaced discharge gates, a sand level signal generator for indicating the level of sand adjacent said gates comprising: adjacent one of said gates a pair of elongated, rod-like elements and means at spaced intervals along said elements for rigidly spacing said elements from each other throughout their length; one of said elementsihaving electrodes spaced therealong; said electrodes being electrically insulated from each other; individual conductor means secured to each of said electrodes; the other of said elements having exposed electrode portions aligned lengthwise of said elements with each of the electrodes of said one element; said other element being a structural support for said one element; and a loW voltage current source electrically connected across said rod-like element and said spaced electrodes; means providing an air gap in the electrical circuit between said current source and said other element, said air gap being of such a .width that the low voltage current Will bridge saidgap when said air gap is filled with sand; said air gap being located insaid hopper adjacent the other of said gates.

References Cited in the file of this patent UNITED STATES PATENTS 1,346,898 Kingsbury July 20, 1920 2,081,650 Tamminga ettal. May 25, 1937 2,261,495 Ewertz Nov. 4, 1941 2,411,309 Whitcomb etal. Nov. 19,1946 2,754,381 Martinet a1. July 10, 1956 2,797,702 Martin July 2, 1957 

